This paper presents a stepwise algorithm for extracting power-lines from mobile laser scanning (MLS) data. This algorithm first extracts non-road points from MLS data by estimating road ranges with regard to scanning mechanism and applying elevation-difference and slope criteria to the road ranges scan-line by scan-line. Then, three filters, in terms of height, spatial density, and size-and-shape, are proposed to extract power-line points in the identified non-road points, followed by Hough transform and Euclidean distance clustering. Finally, a 3D power line is modelled as a horizontal line in X-Y plane and a vertical catenary curve defined by a hyperbolic cosine function in X-Z plane. The proposed algorithm has been tested on a sample of point clouds acquired by a RIEGL VMX-450 MLS system. The results demonstrate the applicability of the proposed algorithm in extracting power transmission lines.